Electric igniter for use in electric initiating devices



Decf4, I l

D. G. ASHCROFT 2,577,501 ELECTRIC IGNITER FOR USE IN ELECTRIC INITIATINGDEVICES Filed April e, 1948 4 sheeis-sheet l Filed April 6, 1948' Dec.4, 1951 ASHCROFT I 2,577,501

ELECTRIC IGNITER FOR USE IN ELECTRIC INITIATING DEVICES 4 Sheets-Sheet 2v Inventor:

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Attorneys.

Dec. 4, 1951 D. G. ASHCROFT 2,577,501

ELECTRIC IGNITER FOR USE IN ELECTRIC INITIATING DEVICES Filed April 6,1948 4 Sheets-Sheet s A ttorn 251 1386- 1951 D. G. ASHCROFT ELECTRICIGNITER FOR USE IN ELECTRIC INITIATING DEVICES 4 Sheets-Sheet 4 FiledApril 6, 1948- INVENTOR" DONALD GEOR'GE ASHCROFT ATTORNEY heads.

Patented Dec. 4, 1951 NIT, srrss ELECTRIC IGNITER FOR USE IN ELECTRICINITIATING DEVICES Donald George Ashcroft, Saltcoats, Scotland, as-

signor to Imperial Chemical Industries Limited, a corporation of GreatBritain Application April 6, 1948, Serial No. 19,356 In Great BritainApril 14, 1947 14 Claims.

The present invention relates to improved electric igniters for use inelectric initiating devices for explosive compositions, incendiarycompositions and the like, and of the kind wherein the pole pieces areconstituted by the bared ends of the insulated leading wires extendingbeyond a spacing element. The invention also relates to an improvedmethod for the produc-- tion of the aforesaid electric igniters.

The present invention does not relate to electric igniters wherein metalfoil elements are united to an insulating sheet element and soldered tothe bared ends of the insulated leading wires.

The term electric igniters as used herein includes structures in themanufacture whereof at least one easily ignitable deflagratingcomposition present in the electric initiating device as well as theresistance element connecting the pole pieces forms an integral part andstructures whereof the resistance element connecting the pole pieces isintended to be embedded in an easily ignitable deflagrating compositionthat is present in the initiating device but does not form part of theigniter structure. The former kind of electric igniter structures areusually referred to as electric fuseheads. Electric fuseheads whereinthe resistance element is a resistance wire embedded in a match headcomposition of non-conducting properties including a deflagratingingredient ignita-ble by the heated resistance wire are known as lowtension fuseheads, while those in which there is no resistance wire butthe match head composition joining the pole pieces includes in additionto the deflagrating ingredient an ingredient rendering itsemi-conducting e. g. graphite, are known as high tension fuse- Thepresent invention is more especially but not exclusively applicable toelectric igniter structures having a resistance wire bridging the polepieces.

In electric igniters of the kind wherein the pole pieces are constitutedby the bared ends of the leading wires the spacing and insulatingelement beyond which the pole pieces extend usually consists of a plugof hard, soft or resilient material cast, moulded or vulcanised around aportion of the two leading wires, at least partly bared where they passthrough the plug, only a short length of the bared portion of each wirebeing allowed to 1 protrude through the plug so that these will be-maintained apart by their own rigidity. When a resilient plug is usedit is ultimately crimped into the casing of an initiating device toform-a waterproof joint. '-This operation tends to introduce a certainelement of uncertainty about the position and spacing of the protrudingbared portions. Electric igniters insulated by means of cast or mouldedhard or soft compositions may also become unserviceable owing todisintegration or flow of the material of the plug. Moreover in themanufacture of the electric igniters some time must elapse before thestructures can be removed from the moulds in which the plugs are cast,moulded or vulcanised.

It is an object of the invention to provide electric igniters of theaforesaid kind wherein relative lateral displacement of the pole pieceswill not occur either on storage or when the electric igniter isinserted into an initiating device.

It is also an object of the invention to provide a more expeditiousmethod of manufacturing electric igniters, and in particular to providea method of fixing portions of the leading wires in the proximity of thepole pieces spaced from one another in parallel relationship on a stripmember by a mechanical operation which can bev repeated at intervalsalong the length of the strip so that subsequent operations can beconducted before the strip is severed to form. individual igniters.

According to the present invention an electric igniter of the kindwherein the pole pieces are constituted by the bared ends of insulatedleading wires extending beyond a spacing element consisting of a stripof compressible material is characterised in that a portion of each ofthe said wires is in the form of an open loop in contact with at leastthe two faces and the four corners of the said strip, with the endportions of the loops on the same face of the strip and each end portionbent over on itself against said face.

These extending bare ends of theleading wires and if desired also theloop forming portions are advantageously flattened.

Preferably the length of the leading wires constituting the loops aswell as their continuations constituting the pole pieces are bare. Inthis case the compressible sheet material must be an insulatingmaterial.

According to the present invention the method for the production ofelectric igniters comprises gripping a length of a strip of compressiblesheet material at intervals along it with an individual pair ofconducting wire lengths each pair consisting of two parallel and spacedinsulated leading wires at least partly bared at their correspondingends by shaping each wire of this pair against the faces and fourcorners of the said strip into an open loop with the end' portions ofthe loop on the same face of the strip and bending over on itself eachend portion against said face.

The bare ends of the end portions of the loop of the wire projectingbeyond one edge of the strip may advantageously be trimmed to length andthe resulting pole pieces may be connected by a resistance wire and/orany match head composition applied in known manner before the strip ofinsulating material is cut.

The open loops may be doubled around the edges of the strip of sheetmaterial, and if desired both edges of the strip may be provided withpairs of spaced notches corresponding to the desired positions to beoccupied by the loops in order to assist in locating said loops.Alternatively the strip of insulating material may be provided with oneor more lines of perforations through which doubled over portions of thepreferably flattened wire representing the commencement and/ortermination of each open loop are passed from one face of the strip andfolded over the other face, preferably so as to bring the points ofrefiection towards one another and thus tightly grip the part of thethickness of the strip between the single portion of the open loop andthe double thickness portions thereof. The strip may consist of forinstance rigid or semi-rigid insulating material into the material ofwhich the wire can be slightly impressed so as to locate the wire loopssecurely in their parallel spaced position. The wires are preferablyflattened before the loops are formed.

It is an advantage of the invention that there is obtained by it acontinuous web structure which can ultimately be cut to form separateigniters, and to which the application of the elements positioned at thepole pieces may be applied before this is done. Another advantage isthat the production of said web can be accomplished as fast as themechanical operations can be carried out with the wire and withoutwaiting for changes in temperature to change the consistency of anymaterial used in the process.

A further advantage is that the length of the strip to be present ineach igniter after the cutting operation and any desired furthertrimming operation may be predetermined so that it will limit the motionof the igniter within the initiator into which it is ultimately insertedand thus prevent the bare wires from touching the walls of theinitiator.

The portion of the preferably flattened leading wires that is formedinto the open loop and caused to embrace the strip of insulatingmaterial may be a portion stripped of its insulation, but alternativelyit may still retain its insulating coating. In the former case the sheetmaterial must be an insulating material. The wires may be flattened bypassing the ends between pressure rollers, and usually if the wires areinsulated when they are passed through the nip the insulation will beruptured as the wires are flattened and can be removed easily when thewires are withdrawn from the nip, as for instance, when the insulatingmaterial consists of a cotton covering.

The wires may be spaced and rendered parallel by pulling them throughguide channels. If

desired the insulated portions near each bare end of the leading wiresmay be partly twisted together and threaded through a plug of preferablyresilient material on to which a' detonator tube or the like willultimately be crimped to provide a waterproof joint.

The strip of compressible sheet material, preferably of insulatingmaterial, may be fed in the direction of its length to a fixed positionat which there is located a combination of suitable folding and pressingtools adapted to apply a pair of the preferably flattened portions ofthe leading wires already brought into spaced parallel relationship,these wires being presented transversely to the strip. As will beunderstood, there may be a series of positions along the path of thestrip at which a series of pairs of spaced and parallel portions of theleading wires are simultaneously applied to the strip by a row ofcombinations of folding and pressing tools. The resulting strip having aseries of. parallel flattened wire loops attached to it may now have thebared ends of the projecting wires trimmed.

If the pole pieces are to be bridged by a resistance wire, the lattermay be attached to the bared ends of the wires, for instance, by spotsoldering or by bending the bare flattened ends of the leading wiresover the resistance wire so as to grip it tightly. A continuous lengthof bridge wire may be used and the unwanted portions in the spacesbetween the pairs of leading wires may be cut off. The attachment of thebridge wire may be carried out as a repetition operation by feeding thestrip to the appropriate tools. The match head composition mayadvantageously be applied to the pole pieces and the bridge wire if usedbefore the strip of insulating material is out.

One form of the invention is further illustrated in the diagrammaticdrawings Figs. 1 through 5, whereof Figure 1 represents a side elevationand Figure 2 a plan view of a pair of leading wires partly twistedtogether and prepared for attachment to an insulating strip. Figure 3 isan isometric view showing a number of pairs of partly twisted leadingwires attached to a strip of press board or the like insulating materialand Figures 4 and 5 show partly sectioned side elevations and plan viewsof a low tension electric fusehead made in accordance with theinvention. Figures. 6 and 7 depict isometrically a, modification of theinvention of Figures 1 and 2.

In the diagrammatic drawings, 2, as is best seen in Figure l, arecylindrical portions of the leading wires covered by textile or. plasticinsulating material I. 3 are flattened, spaced parallel and bared endportions of the wire and 4 is a sheet of pressboard. As is best seen inFigure 3, a space is left on one side of the sheet of insulatingmaterial between the reflexed folds 5 and 6 at the commencement andtermination of the open loop tightly embracing the strip of insulatingmaterial 4. In Figures 4 and 5 numerals i to B have the samesignificance as in Figure 3. I is a tubular plug of resilient waterproofmaterial such as neoprene threaded on to the twisted portion of theinsulated portion of the leading wires.- 8 is a high resistance bridgewire attached by folding over it the extremities of the trimmed ends ofthe pole pieces as shown at I0. 9 is a bead of match composition capableof being ignited by the heat developed in the bridge wire 8 when anelectric current is passed through the latter. The igniter illustratedin Figures 4 and 5 is a low tension electric fusehead, to which acharged detonator tube may be attached by .figures represent amodification of this invention'wherein the strip of insulating material4 is provided with a line of perforations l through which doubled-overportions of the preferably flattened wire 3 representing thecommencement and/or termination of each open loop are passed from oneface of the strip 4 and folded over the other face preferably so as tobring the points of reflection towards one another and thus tightly gripthe part of the thickness of the strip 4 between the single portion ofthe open loop and the double thick portions thereof. Figure 7 representsthe completely formed electric igniter whereas Figures 6 represents theelectric igniter in one stage of its formation.

I claim:

1. An electric igniter wherein the pole pieces are constituted by thebared ends of insulated leading wires extending beyond a spacing elementconsisting of a strip of electrically non-conducting compressiblematerial characterised in that a portion of each of the said wires is inthe form of an open loop in contact with at least the two faces and thefour corners of the said strip, with the end portions of the loops onthe same face of the strip and each end portion bent over on itselfagainst said face.

2. An electric igniter as claimed in claim 1 wherein the said bared endsare flattened.

3. An electric igniter as claimed in claim 1 wherein the open loopportions are flattened.

4. An electric igniter as claimed in claim 1 wherein the said open loopportions are bare.

5. An electric igniter as claimed in claim 1 wherein the continuationsof the loops constituting the pole pieces are bare.

6. A method for the production of electric igniters which comprisesgripping a length of a strip of electrically non-conducting compressiblesheet material at intervals along its length with individual pairs ofconducting wire lengths, each pair consisting of two parallel and spacedinsulated leading wires at least partly bared at their correspondingends, by shaping each wire of this pair against the faces and fourcorners of the said strip into an open loop with the end portions of theloop on the same face of the strip and bending over on itself each endportion against said face.

'7. A method as claimed in claim 6 wherein the bared ends of the endportions of the loop are trimmed to length, then connected by aresistance wire, and thereafter the strip of compressible sheet materialis cut in lengths, each length having gripped thereon one pair ofconducting wire lengths.

8. A method as claimed in claim 6 wherein the said bending over onitself of each end portion is extended to the opposite face of thestrip.

9. A method as claimed in claim 6 wherein op- 5 posite points on thestrip of compressible sheet material are provided with pairs of spacednotches corresponding to the desired positions to be occupied by theloops.

10. A method as claimed in claim 6 wherein the strip of compressiblesheet material is provided with at least one line of perforationsthrough which the doubled end portions of the wire representing thecommencement of each open loop are passed from one face of the strip andfolded over the other face.

11. A method as claimed in claim 10 wherein the said folding is such asto bring the points of reflection towards one another.

12. A method as claim d in claim 6 wherein the bared ends of the wireare flattened before the loops are formed.

13. A method as claimed in claim 6 wherein the spaced and parallelrelationship of the pairs of insulated wires has been effected bypassing the wires through guide channels.

14. A method as claimed in claim 6 wherein the insulated portions neareach bare end of the leading wires are partly twisted together andthreaded through a plug adapted to permit a detonator tube or the liketo be ultimately crimped thereon to provide a waterproof jacket.

DONALD GEORGE ASHCROFT.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,046,816 Lightfoot Dec. 10, 19121,473,866 Phelps Nov. 13, 1923 1,608,005 Schoeppler Nov. 23, 19261,706,659 Fahnestock Mar. 26, 1929 1,970,051 McWeeny Aug. 14, 19342,046,102 Abbott June 30, 1936 2,257,621 Schellenger Sept. 30, 1941FOREIGN PATENTS Number Country Date 543,500 Great Britain Feb. 27, 1942546,533 France Aug. 25, 1922 568,831 Germany Jan. 24, 1933 571,289Germany Feb. 25, 1933

